Method and apparatus for controlling the contours of rolling mill rolls to obtain metal sheet or strip of superior flatness



Feb. 24, 1970 sHlzUo M|zUNo ErAL 3,496,744

METHOD AND APPARATUS RoR coNTRoLLTNG THE coNToURs 0E ROLLING MILL RoLLs To OBTAIN METAL SHEET oR STRIP 0E SUPERIOR -FLATNEss In. .llilA al A uw uw B mvENToRs. sH/zuo M/zu/vo BY MAsAo ANBO M/cmo WASH/DA @caddy/dug@ Arron/vens Feb. 24., 1970 sHlzuo MlzuNo ETAL 3,496,744 METHOD AND APPARATUS FOR CONTROLLING THE CONTOURS OF ROLLING MILL ROLLS TO OBTAIN METAL SHEET OR STRIP OF SUPERIOR FLATNESS 7 Sheets-Sheet 2 Filed Jan. 5l, 1967 FIG.4

PRESSURE P FIG.5

o wwwmhm DEFLECTION S INVENTORS. `Shi/zu@ M/zU/VO MASA 0 ANDO /vncH/o WASH/DA /mmeyag L ATroR/VEKS SHIZUO MlZUNO ETAL Feb. 24., 1970 3,496,744

METHOD ANO APPARATUS FOR OONTROLLING THE cONTOURs OF ROLLING MILL ROLLS To OBTAIN METAL SHEET OR STRIP OF SUPERIOR PLATNEss 7 Sheets-Sheet 3 Filed Jan. 3l. 1967 CONTROLLED VARIABLE COMMANDS V il POWER UN|T CONTROL UNIT ACTUATING SIGNAL SET MECHANISM DETECTING UN IT COMPUTING UNIT .0 A S D S N vl muow We N a WA M WMWAWu m m 00 m v r UAH A n. .Ao MMM Qfu Y B Feb. 24, 1970 sH|zUo MlzUNo ETAL 3,496,744

METHOD AND APPARATUS FOR CONTROLLING THE CONTOURS OF ROLLING MILL ROLLS TO OBTAIN METAL SHEET y OR STRIP OF SUPERIOR FLATNESS Filed Jan. 3l, 1967 '7 Sheets-Sheet 4 FIG.7

ll! rlllllmllllll E aG. coMPARATlvE CEMANDS coMPuTATloN RESULT c o CONTROL MOTOR opme ROLL UNIT VALVE l cRowN 3X5 5K6 3g? D/E s/o vou-AGE AMPL'F'ER TRANsFoRMER TRANsFoRMER I aucKLlNG INDlcAToR FoR MEASUREMENT /Ix B c o E F29 INVENTORS.

SH/zuo M/zuA/o MAsAo A/voo BY MICH/0 wAsH/DA A 7TORNEXS Feb. 24., 1970 SHIZUO MIZUNO EVAL METHOD AND APPARATUS FOR OONTROLLING THE OONTouRs OF ROLLING MILL ROLLS TO OBTAIN METAL SHEET OR STRIP OF SUPERIOR FLATNESS '7 Sheets-Sheet 5 A A F|G.8g C E Flash D C XE x Ki. X L-/J F l 1 1 OISPLACEMENT MEASURING UNIT 54 INDICATING 30 RECORDER DIFFERENTIAL rj 0F Dc TRANSFORMER g o g Z w E BALANCING TYPE m 12 I- z Z l; e g 5 g g; D g 59 E s, o 5 g D D g m O D. n o I D E o o Q n:

o Q E N l 5 s l -1 ELECTRIC SOURCE INVENTORS. SH/z uo M /zuNo MASA o. ANDo M :cH/0 WASH/DA ATTORNEYS Feb. 24, 1970 SHIZUO MIZUNO ETAL METHOD AND APPARATUS FOR CONTROLLING THE CONTOURS OF ROLLING MILL ROLLS TO OBTAIN METAL SHEET OR STRIP OF SUPERIOR FLATNESS Filed Jan. 3l, 1967 '7 Sheets-Sheet 6 FIG. 12 39 S ELECTRIC ELECTRIC ELECTRIC m 29 58 SOURCE SOURCE SOURCE lLI S- S INDICATING RECORDER o Q SLIDING LI. OF DC AUTOMATIC RESISTANCE j\ J\ EALANCING TYPE n: INDICATING RECORDER Q- OF DC AUTOMATIC RsLf$D1lcE I BALANCING TYPE ,t

INDICATING RECORDER z SLIDING m OF DC AUTOMATIC 5 BALANCING TYPE RESSTANCE LL u. 23 12 24 o g X COMPUTING CONTROL UNIT UNIT OPERATION N40 AMPLIFIER CASCADE N I CASCADE SETTER 43 SETTER 43 I I PRESSURE 41. PRESSURE 41 l REGULATOR REGULATOR N 44 I 44 I H PRESSURE X PRESSURE PRESSURE REDUCING -46` PRESSURE REDUCING -46 DETECTOR VALVE OPERA- DETECTOR VALVE OPERA- 45 TING UNIT 45 TING UNIT PRESSURE 47 REDUCING I VALVE S P U HYDRAULIC RES RE CYLINDER REDUC'NG v VE HYDRAULIC CYLINDER FOR CONTRO'- A" FOR CONTROL INVENTORS.

@wel Yug'ez A7'TORNEY5 Feb. 24, 1970 sHlzuo NnzUNo ETAL 3,496,744

.METHOD AND APPARATUS FOR CONTROLLING THE CONTOURS OF ROLLING MILL ROLLS To OBTAIN METAL SHEET,

OR STRIP OF SUPERIORI FLATNESS 7 Sheets-Sheet 7 Filed Jan. s1, 1967 FIG. i3

A sw m @UOH E Tzns M N/NA n wMAw m N000 v v HAI `nited States Patent O METHOD AND APPARATUS FOR CONTROLLING THE CONTOURS OF ROLLING MILL ROLLS TO OBTAIN METAL SHEET OR STRIP OF SUPERIOR FLATNESS Shzuo Mizuno, Masao Ando, and Mlclllol Wasida, Nagoya-shi, Japan, assguors to Sumitomo Light Metal Industries, Ltd., Tokyo, Japan, a corporation of Japan Filed `lan. 31, 1967, Ser. No. 612,869 Claims priority, application Japan, Feb. 5, 1966, l1/6,609; Dec. 29, 1966, 42/357 Int. Cl. B21b 37/04 U.S. Cl. 72-12 3 Claims ABSTRACT OF THE DISCLOSURE This method and apparatus makes non-contacting measurements of internal stress in metal sheet or strip being rolled in a cold rolling mill and utilizes such measurements to precisely bend the rolls to obtain superior sheet atness. This it does by applying loads to a plurality of nozzles which are movable up and down and arranged in a direction transverse to the direction of travel of the sheet or strip running under fixed tension, blowing compressed air against said sheet or strip through said nozzles, thereby producing deflection of said sheet or strip through a layer of air formed between the end surfaces of said nozzles and the adjacent surface. of the sheet or strip, and effecting precise bending of the rolling mill rolls accordmg to the displacement of said nozzles.

As is customarily known, the flatness of the sheet or strip manufactured by passing through the rolls in a rolling mill largely depends on the variation of plate thickness of the sheet or strip on the transverse direction thereof. The main reason for failure to obtain desired atness lies in the buckling of the sheet or strip. It is also known that said buckling is produced from the occurrence of extremely small differences in the diameter of a workroll in its longitudinal direction. By reason of a difference 1n the peripheral speed of the rolls in a longitudinal direction therealong due to the crown of the workroll, the sheet or strip may have a diiference of plastic flow in its transverse direction. This difference tends to produce the difference in the transverse thickness of the sheet or strip which in turn brings about a variety of kinds of buckling lby the restraint exerted on the parts of the sheets which are adjacent to the portion thereof varying in thickness. However, means for automatically controlling the flatness of the sheet or strip without directly contacting it during its rolling has not yet been developed although considerable improvements have been made on automatic gauge control or on the control of various rolling conditions by electronic computer.

The primary reason for the above mentioned situation is that more and mo-re tension is now being applied in the longitudinal direction of the sheet or strip as seen in modern rolling mills and the speed of rolling has so much been accelerated as to cause the rolling mill to be enclosed, whereby measurement of the flatness of the sheet or strip has become far more diiiicult.

Despite these circumstances, a greater degree of perfection is now being demanded for the atness of the product and consequently there has been developed, by the present invention, a measuring apparatus and method for determining the exact condition of flatness of the sheet or strip and for correcting departures from atness during the rolling operation and having high sensitivity and mechanical precision. To this end, the present invention provides means for continuously detecting the buckling conditions of the sheet or strip which is running at a high speed and for correcting the crown of the. workroll so as to get the desired iiatness.

Developments have previously been made aiming toward such a method and apparatus in the attempt to measuse the shape of the sheet or strip during rolling based on the principle that variation of plate thickness in the direction of travel of the sheet or strip corresponds to the variation in its length for a fixed period of rolling time in its longitudinal direction. Hitherto several forms of such apparatus for measuring the buckling of a running sheet or strip under tension have been known but many were found to be unsatisfactory during actual operation.

One of such known methods includes a measurement apparatus in which a plurality of rollers of same shape and arranged in the transverse direction of the. sheet or strip are disposed in the direction vertical to the direction of running of the sheet or strip in contact with but free of sliding relatively to said sheet or strip and thus to record the difference in the peripheral speed of rolls. In another known method the shape of the sheet or strip is measured by considering the difference of tension on the rolls in the transverse direction of the sheet or strip to be equivalent to the difference of deflection of the levels of the rolls since the. difference in the length is considered to be proportional to the difference of tension when the sheet or strip is rolled under tension.

These prior methods, however, are not adequate for rolling a metallic sheet or strip such as aluminum plate which is relatively small in surface hardness and easily injured whenever the rolls come into direct contact with its surface leaving traces on its surface. Usually aluminum sheet or strip owes its excellence to flawlessness, brightness, and smoothness of its surface. Therefore, the primary requisite called for in the measuring apparatus of flatness of the aluminum sheet or strip in rolling is that said apparatus will not contact the surface of the aluminum sheet or strip while it is being rolled.

The principal object of this invention is therefore to provide a method of and apparatus for observing the shape of the sheet or strip in its transverse direction at various points in the course of its running without directly contacting the surface of the sheet or strip and thereby measuring the internal tension of the sheet or strip in order to control the rolling mill.

The further object of this invention s that by using of the newly developed Imethod and apparatus above mentioned, this invention provides a method of and apparatus for measuring the distribution of tension on the sheet or strip in running by automatic control, in which the buckling condition i.e. the lack of flatness of the sheet or strip is measured continuously and the measured value is transformed into adequate information through shape computer circuits and this information is fed back to a known crown control unit such as a workroll bending apparatus whereby the diiference in the plastic flow of the sheet or strip in its transverse direction is cancelled and excellent flatness of the sheet or strip is obtained.

In order that the invention may be more clearly understood an example thereof will now be described with reference to the accompanying drawings, in which:

FIGURES la to lc are diagrammatic views of the sheet or strip showing a variety of bucking conditions and FIGURES ld to 1f show the corresponding distribution of tension in the sheet or strip;

FIGURES 2a, 2b and 2c are diagrammatic views showing the principle of this invention;

FIGURES 3a and 3b are central vertical sections through a portion of the apparatus showing the ow outlet of a nozzle in operation and a condition of the surface of the sheet or strip;

FIG. 4 is a diagrammatic view showing characteristic curves of air layer and pressure load;

FIG. 5 is a diagrammatic view showing deflection of the sheet or strip under tension in which weight is taken as a parameter;

FIG. 6 is a perspective view of one embodiment of a measuring apparatus according to this invention;

FIG. 7 is a front view of the measuring apparatus in FIG. 6;

FIGURES 8a, 8b and 8c show three examples of incipient buckling occurring in the sheet or strip during rolling;

FIGURES 8d, Se and 8f show the respective distributions of stresses therein appearing on tension indicators; and

FIGURES 8g, 8h and 8i show the respective tension graphs recorded thereby;

FIG. 9 is a block diagram showing construction of an automatic control system according to this invention;

FIG. 10 is one example of a block diagram showing a roll bending arrangement;

FIG. 11 is a flow chart showing a system of the measuring unit of the apparatus according to the invention;

FIG. 12 is a flow chart of a hydraulic control unit and FIG. 13 is a diagram showing one example of a crown control unit in use in known workroll bending.

IIt is to be noted that the atness of the sheet or strip is caused from variation of thickness of the sheet or strip in its transverse direction and that the sheet or strip which is of poor quality as regards flatness is termed a buckled sheet or strip. Such buckling in the transverse direction may be classified into three major types as shown in FIG. 1.

There is shown in FIG. la a buckling condition of the sheet or strip in its middle part, the portion buckled being shown in curved line shading. The distribution of internal tension of the sheet or strip in its transverse direction is shown in the accompanying diagram FIG- URE 1d on the right side in the figure.

In that diagram it is shown that said buckled middle part is subjected to compressive stress and that both side portions without buckling are subjected tensile stress.

Bucklings are produced as in FIG. 1b at parts each distant one fourth of the width of the sheet or strip when measured from its side edge when the distribution of tensile and compressive stresses in the transverse direction is as `shown in the diagram thereof in FIGURE 1e. FIG. 1c shows that bucklings are produced along both side edges of the sheet or strip when the distribution of tensile and compressive stresses in the transverse direction of the sheet or strip as is shown in the diagram thereof in FIGURE 1f. These bucklings are usually produced by a slight diterence of diameter in the longitudinal axis of the roll or by the difference in diameter causing a difference in the peripheral speed of the roll due to the crown (or camber), which in turn produces difference of plastic flow in the transverse direction of the sheet or strip and consequently causes a difference of plate thickness in the transverse direction, thereby producing bucklings by restraint thus exerted at the boundaries of said portions of thickness difference.

The sheet or strip thus obtained is elongated by constant tension at the outlet of the rolling mill, whereby there is produced in tensile stress distribution indicated in the stress distribution diagrams of FIGURES la, 1b and 1c including the above internal tensile stress in the transverse direction of the sheet or strip.

Thus this invention has for a further object to provide a method eliminating the buckling resulting from the uneven tensile stress distributiton on the sheet or strip in the transverse direction without being caused to come into contact with the surface of the sheet or strip in the course of its running.

FIGURES 2a, 2b and 2c illustrate the principle of measurement of the buckling described above, in which FIGURE 2a shows that both ends of the sheet or strip are tensioned outwardly and in which the buckling indicated `by which is measured in the absence of tension will disappear when it goes beyond a certain level of tension and the buckling will be levelled off so that its measurement cannot be made visually. FIGURE 2b shows the condition in which a dead weight W is applied at a point on the sheet or strip in its transverse direction. The point at which the dead weight is applied will deflect by The dead weights are applied in the similar way at several points of the sheet or strip in its transverse direction and the magnitude of deflection on such point is compared with the magnitude at each other such point so as to obtain the distribution of tension on the sheet or strip, and thereby to measure the `shape and buckling condition of it.

As hereinbefore described, it is to be understood that the surface condition is primarily important for ensuring good quality sheet or strip such as for aluminum, because the quality affects the value of the product when placed on the market and injuries are liable to be produced easily on the surface of the sheet or strip by slight contact with weight W so as to depreciate the value of the product.

In FIG. 2c, according to the present invention such weight is applied on the sheet or strip through a thin layer of air to allow the weight to exert its load above the sheet or strip without directly contacting it. In fact, this invention has been achieved with this basic principle. In order to produce a bearing effect between the sheet or strip and the weight by interposition of a layer of air, it is required to exert load by blowing jets of compressed air from a nozzle through an outlet so that the nozzle may have the effect of producing a layer of air of xed thickness and pressure between it and the surface of the sheet or strip.

Construction of a nozzle satisfying such requirements is shown in FIGURES 3a and 3b, in which the nozzle 1 is mounted so as to be capable of moving up and down and an air duct Z is provided therein and adapted to have one end connected to a source of compressed air. The nozzle 1 is positioned in a direction at a right angle to the surface of the sheet or strip 3. Each weight 4 is provided with a collar 5 so as to be detachable freely and by its load the nozzle 1 is urged downwardly.

The characteristic features of the nozzle in actual use are shown in FIG. 4, in which relationship of the pressure P of the source of compressed air, the thickness T of the layer of air bearing, and the weight W applied on the sheet or strip is shown.

In operation, the nozzle 1, which has the duct 2 and is movable up and down, is brought near the surface of the sheet or strip step by step in a vertical direction perpendicular to the sheet. Within a certain distance of movement, the force of the jet flow of air acts on the surface of the sheet or strip vertically and downwardly. This force may almost be constant if the surface of the sheet or strip is wide enough for the size of the nozzle. Thus, with the nozzle 1 positioned near the surface of the sheet or strip 3, the space 6 between the surface of the sheet or strip and that of the nozzle becomes smaller and the speed of flow of the air will increase. If, then, said weight 4 is placed on the nozzle 1 and the load produced by its weight acts perpendicularly on the surface of the sheet or strip, the nozzle 1 will be forced downward by the wei-ght applied on the nozzle. As a result, the layer of air in the space 6 will be further cornpressed. The force of the load impressed by the weight W on the nozzle 1 will act on the sheet or strip 3 through the layer 6 of compressed air and will be balanced at some position with the reactionary force of deflection of the sheet or strip, because the layer of compressed air can transmit the load on the nozzle to the sheet or strip Without obstructing said load and thereby produces the deflection of the sheet or strip.

It will be seen from FIGURE 3 that the air blown out from the nozzle 1 will form a strong bearing layer without any direct contact of the nozzle 1 with the sheet or strip 3 and the force applied on the sheet or strip producing its deflection is only affected by the load resulting from the weight 4 placed on the nozzle. At this time, the weight of the nozzle is primarily determined by the magnitude to be produced on deflection of the object to be measured, and the diameter of the nozzle tube, outer diameter of the nozzle, and shape of the surface of the bottom of the nozzle directed to the sheet or strip are determined secondarily accordingly tociror strip of a non-metallic material which is relatively large in the amount of deection.

FIG. 4 is a diagrammatic view showing various characteristics obtained by the measuring unit when the air pressure is less than 3 kg./cm.2 as available for practical use. There are employed two amounts of weight, Iw and IIw for the same nozzle. Regardless of the pressure P, the forces exerted by the weights Iw and IIw on the sheet or strip will be constant. Also it is to be noted that the thickness of the air layer IT and IIT is proportional to the pressure P and inversely proportional to the load W. It is possible however to make the variation in the thickness of the air layer due to variation of the pressure P smaller according to appropriate design.

The relationship of the internal tensile stress a of the sheet or strip under tension and the deflection is shown in FIG. 5 taking the weight W as a parameter. Said relationship of the pressure and the deflection is shown by hyperbolic curve.

In practice, the nozzle 1 of FIGURES 3a and 3b can be designed according to the above mentioned requirements and said measuring apparatuses can be disposed in the direction transverse to the sheet or strip, whereby the distribution of tensile stress on the sheet or strip can be presented as the difference of deilection. By supporting this nozzle to be capable of moving up and down, it will be positioned automatically at a point to balance with the reactionary force of the sheet or strip. By adding the measuring unit indicating said position, the internal tensile stress of the sheet or strip delivered from the rolling mill can well be measured under heavy operational condition.

FIGS. 6 and 7 show one embodiment of the apparatus according to this invention in which the up-and-down displacement of said nozzle is detected by the ditlerential transformer 12 shown in FIGURES 6 and 7. The numeral 3 in FIGURES 3a and 3b indicates an aluminum sheet or strip to be measured under tension. 7, 7', 8 and 8' are workrolls and backup rolls respectively in a fourhigh-strip mill, and 9 indicates a deilector roll.

The measuring apparatus according to this invention is disposed between the workrolls and the deflecter roll. The nozzle 1 is loaded with the weight 4 to be capable of being detached easily, which weight is selected according to the thickness of the sheet or strip. The numeral 10 designates a sliding table for supporting the nozzle and controlling the position of it to the left or the right in sliding. Said sliding table 10 is supported by a base table 11, which is fixed on the frame of the rolling mill parallel to the pass line. In order to electrically transform the upand-down movement of the nozzle 1, a differential transformer 12 is provided on said sliding table 10, and its core 13 is xed to the nozzle 1 through the support arm 14.

Said air duct 2 is ilexibly connected to the source of compressed air 9 by a vinyl or rubber tube 15, and this connection is provided Without restraining the up-and-down movement of the nozzle 1. By constructing the base table 11 in the form of spaced parallel bars (FIGURE 6), the nozzle supporting sliding table 10 is provided with a rectangular lower portion extending downward between these bars for preventing the nozzle 1 from effecting a rotational movement in the peripheral direction while permitting sliding adjustment along the bars.

The buckling condition of the sheet or strip to be measured by the method and apparatus of this invention is shown in FIGURES 8a, 8b and 8c which could not herctofore have been measured under tension of the sheet or strip in a quantitative Way. In FIG. 8a, the sheet or strip in a buckling condition as shown in FIG. l is measured at tive points of A, B, C, D and E in the direction transverse to the sheet or strip. In this case, the internal tensile stress is indicated by the height of a ribbon on the known indicator as shown in FIGURE 8d, and recorded as a distance from the X--X line on the known recorder as shown in FIGURE 8g. Similar indications for FIGURE 8b are Shown in FIGURES 8e and 8h, while those for FIGURE 8c are shown in FIGURES 8f and 8i respectively.

By adjusting the height of the ribbon by making all the portions uniform, it is possible to obtain a sheet or strip of desired ilatness having no internal tensile stress in it.

As above mentioned, the apparatus according to this invention can thus effect a desired prevention of the buckling by thus detecting and measuring its effect while at the same time causing no damage on the aluminum sheet or strip. This operation is easily performed, and thus obtains an extreme advantage for the rolling operation.

Hereinafter, one embodiment of automatic control of the apparatus which effects the above mentioned operation will be described in detail.

FIG. 9 is a block diagram `showing the system of automatic control of the apparatus according to this invend tion. In the diagram object of control 21 represents magnitude of the crown and is controlled by the shape control unit, such as the workroll bending unit or the backup roll bending unit or other shape controlling apparatuses. Detecting unit 22, also shown in FIGURES 3, 6 and 7, is provided for measuring the shape or ilatness of the sheet or strip and the buckling of the sheet or strip corrected with controlled working roll, and these are arranged in the direction transverse to the sheet or strip. At the detecting unit 22, in order to transmit the deflection, it is transformed into electric energy by the differential transformers 12 and it may be transformed into the magnitude of air pressure. A computing unit 23 is provided for transforming deflection into signals and for presenting it in a suitable manner for automatic control or measurement. The unit 23 is capable of making comparative computation of signals emitted from a number of detecting units 22. For this purpose, the deflection may preferably be transformed into electric signals in order to make it more advantageous for the operation of the system and the handling of signals. In the comparative computation commands may be set externally as inputs which may be used for comparison.

The control unit 24 is required to function for transforming the computed signals to signals having adequate magnitude, amount, and respondent speed for driving the power unit 25. Mere provision of a Simple on-oi control will produce a hunting effect which makes it impossible to fully control the system.

To obtain a signal of appropriate magnitude, amount, and respondent speed described above, it is required to provide a function additionally for the control unit 24 to carry on proportional plus integral action or derivative action and to transmit variable and suitable contents for the system. The power unit 25 functions to control the 7 roll shape control unit provided in the rolling mill. If the control of said shape control unit is carried out hydraulically, as described more fully below in connection with FIGURE 13, it may be attained only by opening of the valve, and said opening of valve may be accomplished electrically or by air pressure.

The system is provided to form a complete closed loop so that the workroll may bend microscopically in a con- Vex or concave form according to magnitude of hydraulic pressure or the direction of its operation so as to obtain the sheet or strip of desired atness.

The block diagram shown in FIG. 10 is a detailed example of construction of the apparatus of this invention.

In the diagram, S/D transformer or stress-displacement transformer 26 constitutes a part of the detecting unit 22 described and its actual apparatus is shown in FIG. 6 and FIG. 7. The above-mentioned stress displacement transformer 26 is represented by the air nozzle 1 in FIG. 7 and it functions for transforming the tension of the sheet or strip and its variation into the detecting unit, that is, to the variation in position in vertical direction of the air nozzle 1 corresponding to the variation in the deflection of the sheet or strip.

D/E transformer 27 or displacement-voltage transformer in FIG. 10 acts for transforming the position in the vertical direction, of the detecting unit 1, that is, the position of the air nozzle and the amount of deflection and its variation into voltage, the typical one of which constitutes a differential transformer 12. Depending on circumstances, however, other appropriate electric transformer or air micrometer may be utilized. In this embodiment, as shown in FIGS. 6 and 7, there is provided a differential transformer 12 in the detecting unit.

There is provided an amplifier 28 adapted for obtaining output of adequate magnitude as input for comparative computation and an indicator 29 for measurement. This apparatus is capable of determining detecting sensitivity and adjusting a pass line level.

Detailed example of the above-mentioned amplifier is shown in FIG. ll, in which displacement measuring unit 30 consists of C-R oscillator 31 generating AC voltage for exciting differential transformer 12, an automatic compensating circuit 32 for erasing errors in the power source voltage variation, frequency, temperature, conductor resistance, and linearity, and a measurement adjusting circuit 33 for rectifying output of the differential transformer 12 to introduce output of a fixed AC current.

A zero shifter 34 constitutes a DC millivolt generator for shifting electric zero point of an indicating recorder 29 Of the DC automatic balancing type to a desired position.

The circuitry system is so arranged that 100 v. AC current is rectified and constitutes a constant voltage circuit in use of semi-conductor circuit so as to take out external output through rough and minute adjustment. In FIG. 1l, one of the channels of said indicating recorder 29 of DC automatic balancing type is diagrammatically shown, which is of a ribbon type indicator convenient for observation and which can receive voltage signal from the zero shifter 34, and measure and indicate its value. In practice, the DC automatic balancing type indicating recorder 29 as shown in FIGS. 6 and 10 is required to have five channels in order to measure the distribution of tensile stress on the sheet or strip by the above mentioned detecting unit 1 provided at five places on the sheet or strip in the transverse direction thereof.

In FIG. 10, there is shown an example of the DC automatic balancing indicating recorder 29, which can indicate measurement of the distribution of tension in the direction transverse to the sheet or strip in which the magnitude of tension is proportional to the height of the ribbon. That is, the higher the ribbon, the larger is the tension. It is shown at 29 in FIGURE l() that the tension in the centre part (part C) is smaller than the tension in both end portions (parts A and E) and that the shape of the sheet or strip represents the centre buckling as shown (a) in FIGS. l and 8. Reversely, if the sheet or strip has an edge buckling as shown (c) in FIGS. 1 and 8, the tension on both ends (parts A and E) is srnaller than at the centre part (part C).

The output from the amplifier 28 controls the hydraulic pressure of the control unit 24, said control unit controls the motor 35, and said motor in turn controls the opening of the valve 36 as shown in FIG. 10. Then the roll crown 37 is adjusted in proportion to said opening of the valve, the result of which is fed back to said S/ D transformer 26. More particularly, the output from the amplifier 28 controls the hydraulic pressure of the control unit as shown by the flow chart of FIG. 12.

An explanation will now bemade with reference to FIG. 12. The stress distribution on the strip is detected by the differential transformer 12 at three points of the end of the strip on the driving side, centre part of it, and the end of the strip on the power side, and the measured amount is indicated by the DC automatic balancing indicating recorder 29. The amount of the indication on these points are respectively represented with A, C, and E.

There is provided a sliding resistance 38 on each DC automatic balancing indicating recorder 29. A constant current is applied on both ends of said sliding resistance 38 from a power source box 39 and a voltage signal is taken out in operation representing the indication of each DC automatic balancing indicating recorder 29, that is, of each amount measured A, C and E. Each such amount is transmitted to the computing unit 23 that can compute the formula (A+B) *TMC from said voltage signal as input. The output of this computer unit 23 is used as an input for the control unit 24.

When this control unit 24 is set for the set value of commands such as the control output from the control unit 24 electrically sets the amount of input corresponding to difference of the set amount in the power unit 25. The control unit 24 comprises the following functions. As a control action, it makes a PID (proportional plus integral plus derivation), as an alarm action, three-position action of neutral, high and low. There is provided automatic, manual change-over mechanism and a manual operator.

The output of the` control unit 24 requires an operation amplifier 40 by which it is connected to two units of pressure regulators 41 and 41 (FIGURE 12). The output of the operation amplifier 40 becomes the input of limiters 42, 42. The limiters 42, 42 are provided for distributing the output for control into two systems because the control unit 24 is divided into two systems as described below (FIG. 13 is referred to).

The outputs of the limiters 42, 42 become inputs of the cascade Setters 43, 43'. Cascade Setters `43, 43 function for transforming a current signal to a voltage signal, since the electrical signal to the pressure regulators 41, 41 is a voltage signal.

The voltage outputs of the cascade setters 43, 43' become set signals to the pressure regulators 41, 41. The pressure regulators 41, 41 receive as inputs the output signals from the pressure detecting units 44, 44 described, and also receive as inputs the control outputs of said control unit 24 as set signals to control the pressures in the hydraulic cylinders 45, 45'.

The pressure regulators 41, 41 control the commands according to the instructions received from the control unit 24 so that the cylinder pressure of Imost suitable value may be obtained. It is aided by a three-position action as a controlling action.

The pressure detecting units 44, 44 detect the pressure values in the cylinders 45, 45', transform these pressure values to analog signals (voltage), transmit them and employ them as inputs for the pressure regulators 41, 41.

The pressure reducing valve operating units 46, 46 receive the outputs of the pressure regulators 41, 41 as inputs, operate the pressure reducing valves 47, 47 and regulate the pressure in the cylinders 45, 45. Said pressure reducing valves 47, 47' are operated by gear wheels fixed to the reducing valve controlling handles according to the output signals of the pressure regulators 41, 41', and the -gear wheels are driven by racks according to the magnitude of the output signals and their direction. The output of the control unit 24 is divided into two systems as above mentioned and shown in FIGURE 12, because as shown in FIG. 13, as it loads oil pressure in roll bearings 48, 48', 49 between upper and bottom workrolls 7, 7 and between upper back surface support roll 8 and upper workroll 7, it bends the workrolls 7, 7' to control the crown thereof.

Referring to FIG. 13, if the pressure in the hydraulic cylinders 45, 45 between the upper and bottom workrolls 7, 7 is raised, the workrolls 7, 7 are bent in the direction to which positive crown is applied, and if it is lowered reversely, the workrolls 7, 7 are bent to apply negative crown. In order to bend workrolls 7, 7 by applying negative crown thereto, oil pressure of the hydraulic cylinders 45, 4S may be raised between the bearings 48, 49 of the upper back surface support roll 8 and the upper Workroll 7.

In the above description, there has been given an example setting forth a simple application of the workroll deiiection control unit, in which the signal from the detecting unit 2 controls the workroll deflecting unit with a signal of (A-l-E) T-C accordin-g to the result of measured deflections A, C and E, i.e., the magnitude of tension at the end of the sheet or strip on the driving side, at the centre part, and at the end part of the sheet or strip on its power unit side. It is also possible however to -give such commands from outside, to discriminate and compare outputs at all points and to take them out as control signals at many points with respect to the control unit for controlling the crown at a desired position in the longitudinal direction of the workroll.

What we claim is: 1. A method of continuously measuring internal stress of a resilient metal strip being rolled by the work rolls of a cold rolling mill without contact between the measuring means and the strip during travel of the strip through the mill under a continuously-applied predetermined tension, said method comprising mounting the strip for free and unopposed deflection thereof during travel thereof between successive rolls of the mill,

mounting an air nozzle between said successive rolls and adjacent one side only of the strip for movement perpendicularly thereto toward and away from the strip.

maintaining said nozzle constantly spaced away from and out of contact with the strip,

feeding compressed air at a predetermined pressure through said nozzle and consequently forming a layer of compressed air constantly urging said nozzle away from the strip,

applying a predetermined load to said nozzle and thence through said compressed air layer to the stripand consequently deilecting localized buckling resulting from a difference of plastic iiow in the transverse direction of the strip away from said nozzle while simultaneously causing movement of said nozzle away from the strip,

detecting the magnitude of said movement of said nozzle,

and electrically converting the thus-detected nozzle movement into stress measurement units showing the internal stress within the deected portion of the strip adjacent said nozzle.

V2. A method of continuously controlling the atness of a resilient metal strip being rolled by the work rolls of a cold rolling mill by continuously measuring the internal strip thereof at a plurality of laterally-spaced locations thereacross during travel of the strip through the mill under a continuously-applied predetermined tension, said method comprising mounting the strip for free and unopposed deflection thereof during travel thereof between successive rolls of the mill,

mounting a plurality of air nozzles between said successive rolls in laterally-spaced parallel relationship to one another adjacent one side only of the strip for movement independently of one another perpendicularly toward and away from the strip,

maintaining said nozzles constantly spaced away from and out of contact with the strip,

feeding compressed air at a predetermined pressure through said nozzles and consequently forming layers of compressed air constantly urging said nozzles away from the strip,

applying predetermined loads to said nozzles and thence through said compressed air layers to localized buckling resulting from a difference of plastic flow in the transverse direction of the strip and consequently deecting the strip away from said nozzles while simultaneously causing movement of said nozzles away from the strip,

detecting the magnitude of said movement of each of said nozzles,

converting the magnitude of movement of said nozzles into corresponding electrical signals through arithmetic circuits,

and mechanically deforming the crowns of the work rolls locally in response to said electric signals and thereby achieving flatness of the strip while stabilizing the internal stresses previously existing therein.

3. Apparatus for continuously controlling the iiatness of a resilient metal strip being rolled by the work rolls of a cold rolling mill by continuously measuring the internal stress thereof at a plurality of laterally-spaced locations thereacross between successive rolls of the mill during travel of the stripthrough the mill under a continuously-applied tension, said apparatus comprising means providing free and unopposed deflection of the strip during travel thereof between said successive rolls of the mill,

a base structure adapted to be mounted adjacent one side only of the path of travel of the strip between said successive rolls of the mill,

a plurality of air nozzles mounted on said base structure in laterally-spaced parallel relationship for movement independently of one another perpendicularly to the path of travel of the strip.

means for feeding compressed air at a predetermined pressure to said nozzles and adapted to constantly tform layers of compressed air between said nozzles and the strip and consequently maintaining said nozzles spaced away from and out of contact with the strip,

1 1 12 means for applying predetermined loads to said nozzles v References Cited and thence through said compressed air layers to the strip and adapted to deflect localized buckling re- UNITED STATES PATENTS sulting from a difference ofvplastic flow in the trans- 2,295,399 9/1942 Hanna 73 377 verse direction of the strip away from said nozzles 5 2,728,223 12/1955 Henman 73 37 7 XR While simultaneously causing movement of said noz- 3,026,714 3/1952 Evans el al- 73 37 7 216s away from the Strip, 3,194,055 7/1965 Knobel '13-377 means for detecting the magnitudes of movement of 3,201,985 g /1965 WilliamS 73 37.7 XR Said 11022165, v 3,315,506 4/1967 schneider 72-9 means for converting said magnitudes of movement of l0 3,321,838 5 /1967 Albertson 73 37 5 said nozzles into corresponding electrical signals 3,334,508 3/1967 Martin 72 l2 through arithmetic circuits,

and means for mechanically deforming the crowns of RICHARD Il HERBST, Primary Examiner the work rolls locally in response to said electric GENE P CROSBY Assistant Examiner signals and thereby achieving atness of the strip 15 while stabilizing the varying internal stresses previ- U.S. C1. X.R. ously existing therein. 734-37] i 

